In many engine systems a liquid system is provided which needs to be both filtered and treated with an additive or treatment agent. An example is a lubrication oil system for diesel engines. In some instances, the lubrication oil for diesel engines contains an additive package to extend the life of the oil and to improve engine component protection. The additive package is made up of a variety of chemical compounds designed to perform specific functions in the oil. An example of one of the chemical compounds is zinc dithiophosphate (ZDP), which acts as an oxidation inhibitor in the oil. When the oil is heated in the presence of air (for example in a diesel engine) oxidation occurs, increasing the concentration of organic acids. The ZDP acts to inhibit oxidation, thereby decreasing the rate at which the acid is formed. A measure of the effectiveness of the ZDP in the oil is the “total base number” (TBN). The TBN is an indicator of the amount of acid in the oil. As ZDP becomes used up during engine operation, the TBN changes. At a certain defined TBN level, the oil is generally considered to be too acidic to be left in the engine, and thus needs to be replaced with “fresh” oil.
Diesel engine designs are undergoing changes, as a result of increasing emphasis on reduction of emissions from diesel engines, for example as mandated in the United States by the EPA. In some instances the changes cause acid formation in the oil to be more of an issue with respect to service interval, as compared to diesel engines of the past.
The initial additive package depletes in time. What has been needed has been improvements in approaches that allow for re-addition of the ZDP or similar treatment agents to a liquid (such as oil) under controlled conditions, during normal engine operation.